1. Field of the Invention
The present disclosure relates to a wireless communication device and method, especially to a wireless communication device and method capable of adaptively permitting packet transmission or adjusting a threshold for packet transmission.
2. Description of Related Art
Generally speaking, a wireless device (e.g., a wireless device in compliance with an 802.11 standard) transmits packets through a prescribed channel or one among several prescribed channels. When the wireless device transmits packets, if another wireless device sends packets through the same channel concurrently, the packets from the two wireless devices might interfere with each other, which may cause the packet transmission corresponding to one or both of the two wireless devices to fail. This kind of interference problem is called the packet collision.
In order to avoid packet collision, a plurality of wireless devices in the same network system may adopt the same protocol such as a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol specifying collision detection or collision avoidance regulations. For instance, in a contention-based network system in compliance with the CSMA/CA protocol, once a wireless device wins the transmission opportunity under the contention and starts to transmit packets, the other wireless devices running after the same opportunity should suspend their transmission procedure (e.g., the backoff counting procedure or the procedure of sending packets from a media access control layer circuit to a physical layer circuit) during the transmission duration indicated by the winning wireless device, so as to prevent packet collision.
However, if the wireless devices suspend their transmission procedure due to their transmitting signals whose strengths are too low to make any substantial interference, such suspension does nothing good but causes a waste of network throughput. Therefore, a rule for determining whether the suspension is necessary is necessary. More specifically, in a wireless network system abiding by the same protocol (e.g., the CSMA protocol), a wireless device (hereafter, the concerned device) which shares the same frequency channel with other wireless devices listens to signals from the other devices in the channel. Upon receiving a signal, the concerned device measures the strength of the received signal and compares the strength with a predetermined threshold (e.g., Clear Channel Assessment Threshold (CCA threshold) defined by the protocol). If the comparison result shows that the strength of the received signal falls below the predetermined threshold, the received signal could be treated as noise or something negligible; meanwhile, the concerned device may act as though the channel is clear, and either transmit packets or carry out some appropriate steps that are only permitted when the channel is clear. On the contrary, if the comparison result shows that the strength of the received signal is above the predetermined threshold, this signal should be taken valid; in the meantime, the concerned device is required to treat the channel as it is occupied by a valid signal, and should suspend its transmission procedure for the duration indicated by the received signal.
Through the above-described manner, wireless devices can avoid packet collision. However, in some circumstances, the suspension of transmission could be inappropriate. For instance, if a wireless device is positioned in a noisy environment, the wireless device may suspend its transmission procedure continuously or frequently due to the interference of significant noise. In other words, this wireless device may usually find the transmission channel unclear due to the strength of noise often higher than its predetermined threshold, and thus suspends the transmission procedure for a long while or many a time, which seriously degrades the transmission performance. In another case, a wireless device may find the strength of interference signals (which could be signals irrelevant to normal wireless devices) often higher than its predetermined threshold due to its innate structural characteristic or design or the influence from peripheral devices, and thereby suspends the transmission procedure for a long while or many a time, which stops itself from achieving the expected transmission performance.
In consideration of the above, this industry looks forward to a wireless communication technique capable of dealing with a noisy environment and/or the influence from internal or peripheral signals. Such technique may ensure the performance of wireless transmission or prevent the transmission performance from degrading seriously.